Use of medications by older adults living in the community is far from optimal. Medication errors including over-use, under-use, and misuse are common. The Medicare Modernization Act (MMA) of 2003 required plans to provide medication therapy management (MTM) services to optimize therapeutic outcomes through improved medication use among high risk patients with multiple chronic conditions taking multiple medications. The MMA did not dictate how health plans should deliver MTM and various delivery methods exist. Regardless of delivery method, a model of patient-centered MTM requires that the patient play a pivotal role that includes self-monitoring, self-evaluation, goal setting, and medication-taking. The features of a patient-controlled Personal Health Record (PHR) system parallel and are theorized to enhance these critical patient behaviors. By enhancing patient MTM behaviors, PHRs are theorized to result in enhanced patient-provider communication and care continuity and, in-turn, better prescribing by physicians and better medication adherence by patients. Ultimately, the expected health benefits of enhanced patient MTM behaviors are enhanced treatment effectiveness and reduced adverse effects. The proposed research is a collaboration of the University of Iowa (UI) Older Adults Center for Education and Research on Therapeutics (Iowa CERT) and the Iowa Research Network (IRENE), one of 10 AHRQ primary care practice-based research networks (PBRN). We propose a randomized controlled trial among older adults of the effect of a current representative PHR system on patient-reported MTM behaviors, beliefs about medications, medication-use quality indicators, and on medication adherence. We will also investigate the mechanisms through which PHR may affect the patient MTM behaviors. We theorize that successfully maintaining a PHR provides reinforcement to build self-efficacy for MTM, that the act of keeping a PHR up-to-date increases patient knowledge about medications, and that information gained through using the PHR allows patients to shift the balance of their beliefs about medication from concern toward necessity. Finally, we anticipate that some older adults will have difficulty using a PHR because the user interfaces for existing PHRs are designed for young adults. Declines in cognitive, perceptual and motor abilities among older adults are known to affect their use of computer technologies. Thus, in a human-computer interaction laboratory, we will investigate the usability of the trial PHR system against alternative prototypes developed through participatory design with older adults of varying ability levels.